Water Pollution

Water pollution is the addition/presence of undesirable substances to/in water such as organic, inorganic, biological, radiological, heat, which degrades the quality of water so that it becomes unfit for use’.

Natural sources of pollution of water are soil erosion, leaching of minerals from rocks (due to natural solubility and solubility triggered by acid rain) and decaying of organic matter.

Point and non-point sources of pollution

When pollutants are discharged from a specific location such as a drain pipe carrying industrial effluents discharged directly into a water body it represents point source pollution.

In contrast, non-point sources include discharge of pollutants from diffused sources or from a larger area such as runoff from agricultural fields, grazing lands, construction sites, abandoned mines and pits, etc.

Water Pollution Control Measures

Realising the importance of maintaining the cleanliness of the water bodies, the Government of India has passed the Water (Prevention and Control of Pollution) Act, 1974 to safeguard our water resources.

An ambitious plan to save the river called the Ganga Action Plan was launched in 1985.

In India, the Central Pollution Control Board (CPCB), an apex body in the field of water quality management, has developed a concept of “designated best use”.

Accordingly, the water body is designated as A, B, C, D, E on the basis of

pH,

dissolved oxygen, mg/l

BOD, (200C) mg/l

total coliform (MPN/100ml)

free ammonia mg/l,

electrical conductivity etc.

The CPCB, in collaboration with the concerned State Pollution Control Boards, has classified all the water bodies including coastal waters in the country according to their “designated best uses”.

This classification helps the water quality managers and planners to set water quality targets and identify needs and priority for water quality restoration programmes for various water bodies in the country.

The famous Ganga Action Plan and subsequently the National River Action Plan are results of such exercise.

Riparian buffers: A riparian buffer is a vegetated area (a “buffer strip”) near a stream, usually forested, which helps shade and partially protect a stream from the impact of adjacent land uses.

Treatment of sewage water and the industrial effluents before releasing it into water bodies. Hot water should be cooled before release from the power plants.

Excessive use of fertilisers and pesticides should be avoided. Organic farming and efficient use of animal residues as fertilisers can replace chemical fertilizers.

Water hyacinth (an aquatic weed, invasive species) can purify water by taking some toxic materials and a number of heavy metals from water.

Oil spills in water can be cleaned with the help of bregoli — a by-product of paper industry resembling sawdust, oil zapper, microorganisms.

It has been suggested that we should plant eucalyptus trees all along sewage ponds. These trees absorb all surplus wastewater rapidly and release pure water vapour into the atmosphere.

Bioremediation

Bioremediation is the use of microorganisms (bacteria and fungi) to degrade the environmental contaminants into less toxic forms.

Microorganisms can be specifically designed for bioremediation using genetic engineering techniques.

In situ bioremediation

In situ — It involves treatment of the contaminated material at the site.

Bioventing: supply of air and nutrients through wells to contaminated soil to stimulate the growth of indigenous bacteria.

Biosparging: Injection of air under pressure below the water table to increase groundwater oxygen concentrations and enhance the rate of biological degradation of contaminants by naturally occurring bacteria.

Bioaugmentation: Microorganisms are imported to a contaminated site to enhance the degradation process.

Using bioremediation techniques, TERI has developed a mixture of bacteria called ‘Oilzapper and Oilivorous-S’ which degrades the pollutants of oil-contaminated sites, leaving behind no harmful residues..

Q. Recently, ‘oilzapper’ was in the news. What is it?

It is an eco-friendly technology for the remediation of oil sludge and oil spills.

It is the latest technology developed for under-sea oil exploration.

It is a genetically engineered high biofuel yielding maize variety.

It is the latest technology to control the accidentally caused flames from oil wells.

Answer: a) Current Affairs based question. Keep track of the latest developments.

Ex situ bioremediation

Ex situ — involves the removal of the contaminated material to be treated elsewhere.

Landfarming: contaminated soil is excavated and spread over a prepared bed and periodically tilled until pollutants are degraded. The goal is to stimulate indigenous biodegradative microorganisms and facilitate their aerobic degradation of contaminants.

Bioreactors: it involves the processing of contaminated solid material (soil, sediment, sludge) or water through an engineered containment system.

Composting: Composting is nature’s process of recycling decomposed organic materials into a rich soil known as compost.

Advantages of bioremediation

Useful for the destruction of a wide variety of contaminants.

The destruction of target pollutants is possible.

Less expensive.

Environment-friendly.

Disadvantages of bioremediation

Bioremediation is limited to biodegradable compounds. Not all compounds are susceptible to rapid and complete degradation.

Bioremediation often takes a longer time than other treatment processes.

Q. In the context of solving pollution problems, what is/are the advantage/advantages of bioremediation technique?

It is a technique for cleaning up pollution by enhancing the same biodegradation process that occurs in nature.

Any contaminant with heavy metals such as cadmium and lead can be readily and completely treated by bioremediation using microorganisms.

Genetic engineering can be used to create microorganisms specifically designed for bioremediation.

Select the correct answer using the code given below:

1 only

2 and 3 only

1 and 3 only

1, 2 and 3

Bioremediation is limited to biodegradable compounds.

Answer: c) 1 and 3 only

Phytoremediation

Phytoremediation is the use of plants to remove contaminants from soil and water.

Natural phytoremediation is carried out by mangroves, estuarine vegetation and other wetland vegetation.

Phytoextraction/phytoaccumulation: plants accumulate contaminants into the roots and aboveground shoots or leaves.

Sewage Water Treatment for Domestic Use

Substances that are removed during the process of drinking water treatment include suspended solids, bacteria, algae, viruses, fungi, and minerals such as iron and manganese.

The processes involved in removing the contaminants include physical processes such as settling and filtration, chemical processes such as disinfection and coagulation and biological processes such as slow sand filtration.

Coagulation / Flocculation

Aluminium sulphate (alum) is the most common coagulant used for water purification.

Other chemicals, such as ferric sulphate or sodium aluminate, may also be used.

This causes the tiny particles of dirt in the water to stick together or coagulate.

Next, groups of dirt particles stick together to form larger particles called flocs.

Flocs are easier to remove by settling or filtration.

Sedimentation

As the water and the floc particles progress through the treatment process, they move into sedimentation basins where the water moves slowly, causing the heavy floc particles to settle to the bottom.

Floc which collects on the bottom of the basin is called sludge and is piped to drying lagoons.

In Direct Filtration, the sedimentation step is not included, and the floc is removed by filtration only.

Filtration

Water flows through a filter designed to remove particles in the water. The filters are made of layers of sand and gravel, and in some cases, crushed anthracite.

Filtration collects the suspended impurities in water and enhances the effectiveness of disinfection. The filters are routinely cleaned by backwashing.

Disinfection

Water is disinfected before it enters the distribution system to ensure that any disease-causing bacteria, viruses, and parasites are destroyed.

Chlorine is used because it is a very effective disinfectant, and residual concentrations can be maintained to guard against possible biological contamination in the water distribution system.

The addition of chlorine or chlorine compounds to drinking water is called chlorination.

Chlorine can combine with certain naturally occurring organic compounds in water to produce chloroform and other potentially harmful by-products.

The risk of this is very small, however, when chlorine is applied after coagulation, sedimentation, and filtration.

Ozone gas may also be used for disinfection of drinking water. However, since ozone is unstable, it cannot be stored and must be produced on-site, making the process more expensive than chlorination.

Ozone has the advantage of not causing taste or odour problems. It also leaves no residue in the disinfected water.

The lack of an ozone residue, however, makes it difficult to monitor its continued effectiveness as water flows through the distribution system.

Sludge Drying

Solids that are collected and settled out of the water by sedimentation and filtration are removed to drying lagoons.

Fluoridation

Water fluoridation is the treatment of community water supplies for the purpose of adjusting the concentration of the free fluoride ion to the optimum level sufficient to reduce dental caries.

Fluoride is generally present in all natural water. Its concentration up to a certain level is not harmful. Beyond that level, the bones start disintegrating. This disease is called fluorosis.

We have fluoride problem in many parts of our country. Bureau of Indian Standards prescribes 1.0 mg/l as desirable and 1.5 mg/l as a maximum permissible limit for drinking water.

Defluoridation at domestic level can be carried out by mixing water for treatment with an adequate amount of aluminium sulphate (alum) solution, lime or sodium carbonate and bleaching powder depending upon its alkalinity (concentration of bicarbonates and carbonates in water) and fluoride contents.

pH Correction

Lime is added to the filtered water to adjust the pH and stabilise the naturally soft water in order to minimise corrosion in the distribution system and within customers’ plumbing.

Titbit: National Environmental Engineering Research Institute (NEERI) is at Nagpur.

Removal of iron

In many parts of our country, we have a problem of excess iron in drinking water, especially in North-East regions.

Iron causes bad taste and odour to the drinking water.

Bureau of Indian Standards prescribes desirable limit for iron as 0.3 mg/l.

A major part of iron is oxidised. Then the water is made to react with oxidising media (limestone).

By aeration and further oxidation, the dissolved iron is converted to insoluble ferric hydroxide. The insoluble iron can thus be easily removed through filtration.

Removal of arsenic

Arsenic is found in groundwater in some parts of West Bengal. Arsenic is highly toxic.

Bureau of Indian Standards prescribes desirable limit for arsenic as 0.05 mg/l.

Bleaching powder and alum are used for the removal of arsenic.

Q. Which one among the following industries is the maximum consumer of water in India?

Engineering

Paper and pulp

Textiles

Thermal power

Water consumption by various industries

Thermal power

Textile industry

Paper and Pulp

Iron and Steel industry

Fertilizer Industry

EcoSan toilets

Ecological sanitation is a sustainable system for handling human excreta, using dry composting toilets.

This is a practical, hygienic, efficient and cost-effective solution to human waste disposal.

With this composting method, human excreta can be recycled into a resource (as natural fertiliser), which reduces the need for chemical fertilisers.

Bio-Toilets

Designed by Railways along with DRDO.

Why Bio Toilets in Rail?

Direct discharge of human waste from the existing toilet system in trains causes corrosion of the tracks, costing crores to replace the rail tracks.

The bio-toilets are fitted underneath the lavatories and the human waste discharged into them is acted upon by a particular kind of bacteria that converts it into non-corrosive neutral water.

Terms associated with Bio-Toilets

Bio-digesters: The term biodigester is used for the shells made up of steel for the anaerobic digestion of human waste.

Bio tank: The term bio tank is used for the tanks made up of concrete for the anaerobic digestion of human waste.

Aerobic Bacteria: Aerobic bacteria are those which flourish in the presence of free dissolved oxygen in the wastewater and consume organic matter for their food, and thereby oxidising it to stable end products.

Anaerobic Bacteria: Anaerobic bacteria flourish in the absence of free dissolved oxygen, and survive by utilizing the bounded molecular oxygen in compounds like nitrates (NO3) and sulphates (SO4) etc. thereby reducing them to stable end products along with evolution of foul-smelling gases like H2S (hydrogen sulphide), CH4 (methane).

Facultative Bacteria: Facultative bacteria can operate either as aerobically or as anaerobically.

Anaerobic Microbial inoculums: a mixture of different types of bacteria responsible for the breakdown of complex polymers into simple sugars which are further broken down into low chain fatty acids and finally into biogas.

Anaerobic biodegradation system

Anaerobic digestion is a collection of processes by which microorganisms break down biodegradable material in the absence of oxygen.